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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 70, 2016 - Issue 6
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Original Articles

Theoretical study of air-side volatility effects on the performance of H-type finned heat exchangers in waste heat utilization

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Pages 613-638 | Received 23 Dec 2015, Accepted 01 Apr 2016, Published online: 09 Aug 2016
 

ABSTRACT

In this paper, a comprehensive transient three-dimensional model for heat transfer performance and flow resistance is applied to investigate the characteristics of a fin-and-tube heat exchanger with an H-typed fin. The overall and local dynamic response performance of Nu number and Eu number under volatile flow conditions are analyzed in detail. The results indicate that for the H-typed fin-and-tube heat exchanger, both the heat transfer and the fluid flow are influenced by volatile flow, which consists of three key parameters, time-averaged velocity, volatile amplitude, and the cycle time. Correlations of Nu number and Eu number for each case of volatile flow conditions are presented.

Nomenclature

a=

thermal diffusivity, m2 s−1

A=

heat transfer area, m2

Ac=

cross-sectional area, m2

Au=

oscillation amplitude

cp=

fluid specific heat, J kg−1 K−1

D=

tube outside diameter, m

De=

equivalent diameter, m

Fp=

fin pitch, m

Ft=

fin thickness, m

h=

heat transfer coefficient, W m−2 K−1

H=

fin height, m

N=

tube row number

p=

pressure, Pa

P=

wetting perimeter, m

qm=

mass flow rate, kg s−1

Q=

heat transfer rate, W

S1=

spanwise tube pitch, m

S2=

longitudinal tube pitch, m

t=

time, s

T=

temperature, K

ΔTm=

logarithmic-mean T difference, K

Tu=

oscillation period, s

u, v, w=

x, y, z velocity components, m s−1

U=

velocity magnitude, m s−1

W=

slit width, m

x, y, z=

Cartesian coordinates

Greek symbols=
λ=

thermal conductivity, W m−1 K−1

ν=

kinematic viscosity, m2 s−1

ρ=

fluid density, kg m−3

Dimensionless numbers=
Re=

Reynolds number

Nu=

Nusselt number

Eu=

Euler number

Subscripts=
in, out=

channel inlet and outlet

w=

fin surface

max=

maximum value

min=

minimum value

Nomenclature

a=

thermal diffusivity, m2 s−1

A=

heat transfer area, m2

Ac=

cross-sectional area, m2

Au=

oscillation amplitude

cp=

fluid specific heat, J kg−1 K−1

D=

tube outside diameter, m

De=

equivalent diameter, m

Fp=

fin pitch, m

Ft=

fin thickness, m

h=

heat transfer coefficient, W m−2 K−1

H=

fin height, m

N=

tube row number

p=

pressure, Pa

P=

wetting perimeter, m

qm=

mass flow rate, kg s−1

Q=

heat transfer rate, W

S1=

spanwise tube pitch, m

S2=

longitudinal tube pitch, m

t=

time, s

T=

temperature, K

ΔTm=

logarithmic-mean T difference, K

Tu=

oscillation period, s

u, v, w=

x, y, z velocity components, m s−1

U=

velocity magnitude, m s−1

W=

slit width, m

x, y, z=

Cartesian coordinates

Greek symbols=
λ=

thermal conductivity, W m−1 K−1

ν=

kinematic viscosity, m2 s−1

ρ=

fluid density, kg m−3

Dimensionless numbers=
Re=

Reynolds number

Nu=

Nusselt number

Eu=

Euler number

Subscripts=
in, out=

channel inlet and outlet

w=

fin surface

max=

maximum value

min=

minimum value

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